Opaque universe gives insight into galaxy formation

A new study sheds light on both the cosmic web, as well as what the universe was like when the first galaxies formed.

Researchers from numerous California universities found that 12.5 billion years ago the most opaque place in the universe had almost no matter, a new study in the Astrophysical Journal reports.

Almost all of the universe contains a vast, web-like network of dark matter and gas. Known as the “cosmic web,” that lattice accounts for most of the matter in the universe.

Though the gas within the network is almost completely transparent because it is kept ionized by ultraviolet radiation, it was not always that way.

Researchers first found that information roughly 10 years ago, when they realized 1 billion years after the Big Bang the gas hanging throughout the cosmos was not only opaque as a result of ultraviolet light, but also that its transparency changed greatly from region to region.

Then, a few years past that finding, the team behind the recent research found that the differences in opacity were so large that either the amount of gas — or the radiation in which it sits — also shifted in each area.

“Today, we live in a fairly homogeneous universe,” said lead author George Becker, a researcher from the University of California, Irvine, according to Science Daily. “If you look in any direction you find, on average, roughly the same number of galaxies and similar properties for the gas between galaxies, the so-called intergalactic gas. At that early time, however, the gas in deep space looked very different from one region of the universe to another.”

To take a closer look at the notable differences, scientists used the Subaru telescope in Hawaii to search for galaxies in a vast, 300-light-year stretch of the universe where intergalactic gas was extremely opaque.

In terms of the cosmic web, more opacity typically equals more gas, which means more galaxies. However, in the study the team found the exact opposite. The region they analyzed, despite being opaque, had much less galaxies on average.

Though they are not sure why that is, the researchers postulate it is because UV light could not travel very far in the early universe. As a result, any section with only a few galaxies would look much darker than one with more activity.  

This discovery is important because it could help scientists gain insight into the first billion years after the Big Bang, when ultraviolet light from the first galaxies filled the universe and permanently transformed the gas in deep space. In addition, analyzing deep space galaxies may also shed light on how the cosmic web first came to be. 

“There is still a lot we don’t know about when the first galaxies formed and how they altered their surroundings,” said Becker, according to SciTechDaily.

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